We have observed that immune complexes isolated from Plasmodium berghei-infected mice effectively inhibit Fc- receptor - mediated phagocytosis. We now propose to determine whether this is a general phenomenon for malarial immune complexes. We will isolate immune complexes from squirrel monkeys (Saimiri sciureus) and humans with P. falciparum and P. vivax and determine whether such complexes mediate or inhibit immune phagocytosis. In addition, we will determine whether antibody-dependent cytotoxicity (ADCC) is mediated or inhibited by these complexes. We will also analyze the antigens, immunoglobulin isotypes, complement components, and size of immune complexes isolated from P. falciparum and P. vivax infected monkeys and humans and from P. chabaudi-infected mice. We will try to correlate the biological effects of complexes with: the stage in the cycle that the antigen is associated with, the Ig isotypes, the presence of complement, and whether the complexes are associated with chronic or acute infections. In addition, we will try to determine whether the antigens involved in the immune complexes are among the "protective" antigens or are unique to the immune complexes.